The invention relates to a presser bar pressure control module for a sewing machine.
There are in the prior art a substantial number of devices for regulating the pressure exerted by a sewing machine presser bar on a work fabric to facilitate fabric feeding. There is, for example, the U.S. Pat. No. 3,055,326, issued on Sept. 25, 1962, which discloses a presser bar having a hollow interior supporting a compression spring against which bears a plunger having an out turned arm terminating in a finger in engagement with a pressure regulating cam rotatably supported on a bracket affixed to the sewing machine frame. In this device the force applied to the spring by the cam is offset from the spring axis, giving rise to a possibility of cocking and binding of the plunger resulting in erratic pressure. In this device also careful assembly is required to insure proper engagement of the finger on the out turned arm of the plunger with the pressure regulating cam.
In the U.S. Pat. No. 3,294,047, issued on Dec. 27, 1966, there is disclosed a device having a hollow presser bar within which is supported a compression spring against which bears a plunger. The end of a lever, pivoted on a sewing machine frame, bears on the end of the plunger, with an intermediate portion of the lever having a cam follower element in engagement with a pressure regulating cam rotatably supported by the sewing machine frame. Such an arrangement requires the separate assembly or disassembly of individual components on the sewing machine frame, a tedious process required each time access to the interior of the head end of the sewing machine is required.
In the U.S. Pat. No. 3,793,696, issued on Feb. 26, 1974, is disclosed a pressure control module supporting a pressure regulating cam operating through lever arrangements to wind up a spiral spring having one end impinging on a roller carried on a side of a block affixed to a presser bar. This arrangement, while having the desirable modular construction presents some difficulties in effecting engagement of the end of the spiral spring with the roller during assembly, and also applies the spring force offset from the presser bar axis, giving rise to side loading of the presser bar inducive to cocking and binding.
What is required is a presser bar pressure control module capable of ready and carefree disassembly and assembly, which will operate in axial alignment with a presser bar and compression spring to preclude any possibility of binding and cocking.